Water Resources - Quick Reference

Global Water Resources

  • Oceans hold 97.22%97.22\% of Earth's water; freshwater 2.78%2.78\%.

  • Freshwater breakdown: water bodies 0.47%0.47\%, atmospheric water 0.03%0.03\%, belowground water 22.22%22.22\%, ice and glaciers 77.28%77.28\%.

Water Availability and Use

  • Water is abundant but usable water is rare.

  • World fresh water use: 70%70\% agriculture; 30%30\% split between industry (≈20%20\%) and households (≈10%10\%).

  • Over the past 50 years50\,\text{years}, water for irrigation has doubled.

  • U.S. uses about one-third of all freshwater; the U.S., India, and China account for roughly 50%50\% of irrigated land.

Sectoral Water Use

  • Agriculture: largest user of water worldwide, ≈70%70\%.

  • Industry: second largest, ≈20%20\%; uses include electricity generation, cooling machinery, refining metals and paper.

  • Households: third largest, ≈10%10\%; in the U.S., indoor use is similar across states; outdoor use varies.

Water Distribution and Access

  • Earth’s water is not evenly distributed; 2×1092\times 10^9 people (20%) lack access to clean drinking water.

  • About 1.8×1061.8\times 10^6 people die from diarrheal diseases annually due to contaminated water.

  • The future depends on resolving ownership, improving conservation, and developing water-saving technologies.

Global Access to Safe Water (2000-2020)

  • >2 billion people use a drinking water source contaminated with feces.

  • Globally, women and girls spend 2×108 hours/day2\times 10^8\,\text{hours/day} collecting water.

  • 1.7×1091.7\times 10^9 people lack access to a toilet (≈1/4 of population).

Groundwater and Aquifers

  • Aquifers: small spaces in permeable rock or sediment that store water.

  • Unconfined aquifers: porous rock covered by soil.

  • Confined aquifers: surrounded by impermeable rock or clay.

Groundwater Concepts

  • Recharge area; water table; confining layer (impermeable); confined aquifer; unconfined aquifer; well; groundwater flow.

Cone of Depression and Pumping Effects

  • Cone of depression: area where groundwater is no longer present due to pumping.

  • Before pumping: balanced water table; after heavy pumping: lowered water table.

Ogallala Withdrawals

  • Groundwater withdrawals map categories by million gallons per day:

    • 0−20000-2000

    • 2001−50002001-5000

    • 5001−100005001-10000

    • 10001−2000010001-20000

    • 20001−2880020001-28800

Saltwater Intrusion

  • Saltwater intrusion occurs when pumping fresh water faster than recharge near coastal areas.

Water Ownership and Conservation

  • Water ownership: people can have rights to water use but do not own the water.

  • Population growth may increase water conflicts.

  • Conservation: use efficient fixtures, faucets, and washing machines; xeriscaping to reduce irrigation.

Local Colorado Water Facts

  • Greeley/Evans drinking water costs 0.006$/gallon0.006\$/gallon.

  • Water comes from snowmelt.

  • All water is owned in Colorado; water rights are a major issue at CU Boulder.

Water Terms

  • Potable water: clean, drinkable water.

  • Gray water: used water from showers, laundry, etc.; may be recycled for toilets, car washing, irrigation.

  • Black water: used water from toilets.

  • Gray water use in Sydney, Australia saves up to 5×104 L/year5\times 10^4\,\text{L/year} per household.